Stewart-Warner, a radio and automotive instrument manufacturer, used the name “Magic Keyboard” back in the 1930s.
If they trademarked that name, it would have been trademarked in a different industrial category. Unlikely they've kept up paying the trademark license for almost eighty years either. However, while Apple may have already Trademarked "Magic Keyboard" for a future product, I haven't seen any evidence of such a thing. Apple received an international Trademark for "Magic Toolbar" under a Netherlands shell company last year along with some others which are at this point still unknown. They do this to keep future products as secret as possible until they are ready to reveal them. They then transfer the Trademark to Apple USA when the product is ready for announcement. Next time it might be a French or German shell corporation that applies for the Trademark.
I put up an article a week or so ago about the discovery of the "Magic Toolbar" Trademark by a blogger who tracks trademark transfers.
The “Mother of all Demos”, presented by Douglas Engelbart (1968)
https://www.youtube.com/watch?v=yJDv-zdhzMY
Oh, incidentally, Apple was granted a patent a couple of years ago for an entire moveable key, haptic feed back keyboard in which the entire keyboard was a touch screen that could be changed instantly, modifying the look, purpose, and layout of each key, and also become an entire mutitouch track pad as various apps modified the needs of input. That will probably, one day, be released as the “Magic Keyboard.”